Exhaust gas purification device for internal combustion engine

ABSTRACT

An exhaust gas purification device of a diesel engine having a DPF (diesel particulate filter) for collecting particulate matters such as soot and unburned components from exhaust gas of the diesel engine calculates an oil dilution quantity as a quantity of fuel diluting engine oil from a regeneration time of the DPF and an operation state. The exhaust gas purification device alleviates an increase in the oil dilution quantity by using a regeneration device that causes the oil dilution quantity less than the oil dilution quantity caused by another regeneration device when the oil dilution quantity exceeds a predetermined value. Thus, both of suppression of the oil dilution quantity and inhibition of deterioration of fuel consumption due to post-injection can be achieved.

CROSS REFERENCE TO RELATED APPLICATION

This application is based on and incorporates herein by reference Japanese Patent Application No. 2007-144844 filed on May 31, 2007.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an exhaust gas purification device of an internal combustion engine having a diesel particulate filter (also referred to as a DPF) in an exhaust pipe for exhaust purification.

2. Description of Related Art

There is a conventional technology of a post-injection for sending additional fuel directly into a DPF in order to effectively combust particulate matters in the DPF by injecting the additional fuel in an expansion stroke after a main injection of an engine when a deposition quantity of the particulate matters in the DPF exceeds a predetermined value, for example, as described in Patent document 1 (Japanese Patent Application No. H08-42326) or Patent document 2 (Japanese Patent Application No. 2005-307746). The particulate matters are soot, unburned matters and the like contained in exhaust gas of the engine.

However, since the post-injection is performed during the expansion stroke, the injected fuel is hard to evaporate and tends to adhere to a wall surface of a cylinder. The fuel adhering to the wall surface of the cylinder descends through a gap between a piston ring and the cylinder, causing a problem of engine oil dilution.

Furthermore, if the post-injection is repeatedly performed for a long time and the quantity of the fuel diluting the oil (referred to as an oil dilution quantity, hereinafter) becomes excessive, there is a possibility that lubrication of the piston is deteriorated or vaporized fuel enters an air intake side, causing a problem of increase in engine rotation speed.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide an exhaust gas purification device of an internal combustion engine capable of achieving both of inhibition of oil dilution and inhibition of fuel consumption deterioration due to a post-injection.

According to an aspect of the present invention, an exhaust gas purification device of an internal combustion engine having a diesel particulate filter for collecting particulate matters contained in exhaust gas of the engine has a controller, a particulate matter deposition quantity measurement section, a particulate matter deposition quantity determination device, an oil dilution related data measurement device, an oil dilution related data determination device, and a regeneration device. The controller controls operation of the exhaust gas purification device. The particulate matter deposition quantity measurement section measures a deposition quantity of the particulate matters in the diesel particulate filter. The particulate matter deposition quantity determination device determines whether the deposition quantity of the particulate matters measured by the particulate matter deposition quantity measurement section is greater than a first predetermined value. The oil dilution related data measurement device measures oil dilution related data necessary for deriving an oil dilution quantity as a quantity of fuel diluting engine oil. The oil dilution related data determination device determines whether the oil dilution related data measured by the oil dilution related data measurement device is greater than a second predetermined value. The regeneration device combusts the particulate matters to regenerate the diesel particulate filter. The regeneration device includes a first regeneration device and a second regeneration device. The second regeneration device causes the oil dilution quantity less than the oil dilution quantity caused by the first regeneration device and causes a fuel consumption rate greater than the fuel consumption rate caused by the first regeneration device.

The controller has a selection device. The selection device selects the first regeneration device from the two regeneration devices when the particulate matter deposition quantity determination device determines that the particulate matters greater than the first predetermined value in quantity are deposited in the diesel particulate filter and the oil dilution related data determination device determines that the measured oil dilution related data is lower than the second predetermined value. The selection device selects the second regeneration device from the two regeneration devices when the particulate matter deposition quantity determination device determines that the particulate matters greater than the first predetermined value in quantity are deposited in the diesel particulate filter and the oil dilution related data determination device determines that the measured oil dilution related data is higher than the second predetermined value.

With the configuration, the exhaust gas purification device can selectively use the first regeneration device, which causes the large oil dilution but the small fuel consumption deterioration, and the second regeneration device, which causes the small oil dilution but the large fuel consumption deterioration, based on the present oil dilution quantity in the engine. Thus, the exhaust purification device can inhibit the fuel consumption deterioration while controlling the oil dilution quantity to or under the predetermined value. That is, the exhaust gas purification device exerts an effect of achieving both of inhibition of the oil dilution and inhibition of deterioration of the fuel consumption during the DPF regeneration.

According to another aspect of the present invention, the first regeneration device performs post-injection for injecting the fuel in an expansion stroke, and the second regeneration device performs the post-injection at injection timing advanced from injection timing in the case of the first regeneration device in the expansion stroke.

With the configuration, the exhaust gas purification device can have the two regeneration devices of the first regeneration device, which causes the large oil dilution but the small fuel consumption deterioration, and the second regeneration device, which causes the small oil dilution but the large fuel consumption deterioration, even without providing any specific external device. That is, the two kinds of the regeneration devices can be provided without necessitating an extra cost.

According to another aspect of the present invention, the post-injection is performed as a plurality of injections performed in a plurality of times during the expansion stroke.

With the configuration, a quantity of the post-injection per one injection can be reduced even if the total post-injection quantity is the same. Thus, the quantity of the fuel adhering to the cylinder can be reduced and the oil dilution quantity can be reduced.

According to another aspect of the present invention, the oil dilution related data measurement device measures the oil dilution related data from vehicle speed and a travel distance in a period in which the first regeneration device or the second regeneration device is operated or from the vehicle speed and a travel time in a period in which the first regeneration device or the second regeneration device is operated.

The DPF regeneration time lengthens and the oil dilution quantity increases when the vehicle speed is low and exhaust temperature is low. With the above configuration, the oil dilution quantity can be calculated from the relationship.

According to another aspect of the present invention, the oil dilution related data measurement device measures the oil dilution related data from a duration in which the first regeneration device or the second regeneration device is operated.

Generally, the oil dilution quantity increases if the DPF regeneration time lengthens. With the above configuration, the exhaust purification device can derive the oil dilution quantity from the DPF regeneration time.

According to yet another aspect of the present invention, the oil dilution related data measurement device derives the oil dilution related data from a difference between the oil dilution quantity and an oil evaporation quantity as a quantity of the fuel evaporating from the oil.

With the configuration, the oil dilution quantity can be derived accurately from the difference between the oil dilution quantity and the oil evaporation quantity.

BRIEF DESCRIPTION OF THE DRAWINGS

Features and advantages of embodiments will be appreciated, as well as methods of operation and the function of the related parts, from a study of the following detailed description, the appended claims, and the drawings, all of which form a part of this application. In the drawings:

FIG. 1 is a system diagram showing an exhaust gas purification device of an internal combustion engine according to a first embodiment of the present invention;

FIG. 2 is a schematic diagram showing a construction example of an ECU according to the first embodiment;

FIG. 3 is a flowchart showing regeneration processing of a DPF according to the first embodiment;

FIG. 4A is a diagram showing a relationship between a crank angle and an opening degree of an injector in the case of a first regeneration device according to the first embodiment;

FIG. 4B is a diagram showing a relationship between the crank angle and the opening degree of the injector in the case of a second regeneration device according to the first embodiment;

FIG. 5A is a diagram showing a comparison example of temperature in a cylinder between the case of the first regeneration device and the case of the second regeneration device according to the first embodiment;

FIG. 5B is a diagram showing a comparison example of an oil dilution quantity between the case of the first regeneration device and the case of the second regeneration device according to the first embodiment;

FIG. 5C is a diagram showing a comparison example of fuel consumption deterioration between the case of the first regeneration device and the case of the second regeneration device according to the first embodiment;

FIG. 6 is a flowchart showing regeneration processing of a DPF according to a second embodiment of the present invention;

FIG. 7A is a diagram showing a change in an oil evaporation quantity due to engine coolant temperature and an oil dilution quantity according to the second embodiment;

FIG. 7B is a diagram showing a change in the oil dilution quantity due to engine output torque and engine rotation speed according to the second embodiment; and

FIG. 8 is a diagram showing a relationship between a difference between the oil evaporation quantity and the oil dilution quantity and a travel time or a travel distance according to the second embodiment.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

Now, a first embodiment of the present invention will be described with reference to drawings. FIG. 1 is a system diagram showing an exhaust gas purification device of an internal combustion engine 1 according to the present embodiment. A diesel engine 2 shown in FIG. 1 serves as a motor. An airflow meter 3 for measuring a flow rate of an air on an intake side of the diesel engine 2, an engine rotation sensor 4 for measuring rotation speed NE of the diesel engine 2, and an accelerator position sensor 5 for measuring a position ACC of an accelerator achieved by a driver are provided as sensors for determining a state of the diesel engine 2. The diesel engine 2 has an injector including a fuel injection valve for injecting fuel. The injector is electrically connected to an ECU 10 (engine control unit) as a control unit. The ECU 10 manages an opening degree and timing of the fuel injection valve of the injector for injecting the fuel. The airflow meter 3, the engine rotation sensor 4 and the accelerator position sensor 5 are also electrically connected to the ECU 10 as the control unit and transmit measurement values to the ECU 10. The ECU 10 grasps and manages the engine state based on the measurement values.

Exhaust temperature sensors 6 for measuring exhaust temperature TE, an oxygen concentration sensor 7 for measuring an oxygen concentration of the exhaust gas between the diesel engine 2 and a DPF 9 for removing particulate matters, and a differential pressure sensor 8 (a particulate matter deposition quantity measurement section) for measuring pressure difference ΔP of the exhaust gas across the DPF 9 are provided as sensors for acquiring information about exhaust gas from the engine. The exhaust temperature sensors 6, the oxygen concentration sensor 7, and the differential pressure sensor 8 are also electrically connected to the ECU 10 as the control unit like the engine rotation sensor 4 and the accelerator position sensor 5 and transmit measurement values to the ECU 10. The transmitted measurement values are used for grasping the state of the engine. The differential pressure ΔP measured by the differential pressure sensor 8 is used for determining a particulate matter deposition quantity PM of the DPF 9.

FIG. 2 is a schematic diagram showing a construction example of the ECU 10 according to the present embodiment. The ECU 10 consists of CPU 20 for controlling respective components, ROM 21 for storing control programs, various data and the like, RAM 22 serving as a workspace for the computation performed by the CPU 20, and EEPROM 23 as a nonvolatile memory for saving various settings. The components of the ECU 10 exchange the data through a bus 50. Electric connection with exteriors such as the sensors is made through the bus 50 and an I/O 51.

The ROM 21 stores a particulate matter deposition quantity calculation program 31 (a particulate matter deposition quantity determination device) that calculates a quantity of the particulate matters deposited on the DPF 9 (i.e., the particulate matter deposition quantity PM) from the differential pressure ΔP measured with the differential pressure sensor 8, a DPF temperature control program 32 that controls temperature of the DPF 9 through the post-injection during the regeneration of the DPF 9, an operation state measurement program 34 (an oil dilution related data measurement device) that measures vehicle speed, travel distance and travel time as data for calculating an oil dilution quantity Qd, an oil evaporation quantity calculation program 35 (the oil dilution related data measurement device) that calculates a quantity of the fuel evaporating form the oil (i.e., an oil evaporation quantity Qv) based on engine coolant temperature Teng and the oil dilution quantity Qd, an oil dilution quantity calculation program 36 (the oil dilution related data measurement device) that calculates the oil dilution quantity Qd from the engine rotation speed NE and engine output torque TOR, and a DPF regeneration time measurement program 37 (the oil dilution related data measurement device) that measures a regeneration time TRdpf of the DPF 9.

The CPU 20 executes various types of processing by deploying the contents of the ROM 21 to the RAM 22. The CPU 20 executes various types of processing by deploying the values of the various settings necessary for the processing from the EEPROM 23 to the RAM 22. When there is change to the settings, the CPU 20 saves the settings by writing the changed values in the EEPROM 23.

Next, control of the post-injection during the regeneration of the DPF 9 according to the present embodiment will be explained with reference to a flowchart. The regeneration processing of the DPF 9 according to the present embodiment is processing for combusting and removing the particulate matters in the DPF 9 when the particulate matter deposition quantity PM collected by the DPF 9 exceeds a predetermined value. In the present embodiment, the post-injection is performed after a main injection and the particulate matters deposited on the DPF 9 is removed by combustion such as the combustion of the fuel of the post-injection. Thus, the DPF 9 is regenerated.

FIG. 3 is a flowchart showing the regeneration processing of the DPF 9 according to the present embodiment. First, in S100 of the flowchart, the ECU 10 determines whether the particulate matter deposition quantity PM of the DPF 9 is greater than a first predetermined value a requiring the regeneration of the DPF 9. The determination is performed with the use of a publicly known technology. The publicly-known technology is, for example, a method of measuring the pressure difference ΔP between the inlet and the outlet of the DPF 9 with the differential pressure sensor 8 and by estimating the particulate matter deposition quantity PM. The differential pressure ΔP measured by the differential pressure sensor is large when the particulate matter deposition quantity PM is large. It is determined that the particulate matter deposition quantity PM of the DPF 9 is greater than the first predetermined value a when the pressure difference ΔP exceeds a prescribed value. If it is determined that the particulate matter deposition quantity PM is equal to or less than the first predetermined value a in S100 (S100: NO), the ECU 10 enters a waiting state until the determination of whether the particulate matter deposition quantity PM is greater than the first predetermined value a requiring the regeneration of the DPF 9 is performed next time.

If it is determined that the particulate matter deposition quantity PM is greater than the first predetermined value a requiring the regeneration of the DPF 9 in S100 (S100: YES), the ECU 10 starts the regeneration of the DPF 9 in S110. When the regeneration of the DPF 9 is performed, the post-injection is performed to send unburned fuel to the DPF 9 with the exhaust gas, and the particulate matters in the DPF 9 are combusted with oxidization heat of an oxidation catalyst supported by the DPF 9. Thus, the quantity of the particulate matters deposited on the DPF 9 decreases. The deposition of a large quantity of the particulate matters hinders the stream of the exhaust gas, lowering an engine output. Therefore, the regeneration is indispensable for the DPF 9. The particulate matters begin to combust at approximately 550 degrees C.

Performing the post-injection during the regeneration means that the fuel is injected into the cylinder in a state where the piston has descended after passing a top dead center and that the fuel adheres to a cylinder wall. The fuel adhering to the cylinder wall causes the oil dilution as mentioned above. In such the case, there is a possibility that the adhering fuel causes defective lubrication of the piston or a phenomenon that the vaporized fuel enters the air intake side and the engine rotation speed rises.

In order to avoid the above-mentioned phenomena, the ECU 10 determines whether the oil dilution quantity Qd as the quantity of the fuel diluting the engine oil is greater than a predetermined quantity in S120. Since it is difficult to directly measure the oil dilution quantity Qd, it is determined whether the oil dilution quantity Qd is greater than the predetermined quantity based on the operation condition. For example, emission of low-temperature exhaust gas is continued when low-speed operation is continued for a predetermined time or over. This causes a large quantity of the unburned fuel to adhere to the cylinder wall, advancing the oil dilution. Therefore, when the low-speed operation is continued for the predetermined time or over, it is determined that the oil dilution quantity Qd is greater than the predetermined quantity in S120 (S120: YES). For example, in the present embodiment, it is determined that the oil dilution quantity Qd is greater than the predetermined quantity on a condition that operation at the vehicle speed of 20 km/h or lower continues for 60 minutes or over. The condition for determining whether the oil dilution quantity Qd is greater than the predetermined quantity is not limited to this condition.

For example, it may be determined that the oil dilution quantity Qd is greater than the predetermined quantity on a condition that the low-speed operation is continued for a predetermined distance or over. In the present embodiment, for example, a condition that the operation at the vehicle speed of 20 km/h or lower continues for a distance of 20 km or over may be used for the determination. The condition for determining whether the oil dilution quantity Qd is greater than the predetermined quantity is not limited to this condition.

If the ECU 10 determines that the low-speed operation is not continued, i.e., if the ECU 10 determines that the oil dilution quantity Qd is not greater than the predetermined quantity in S120 (S120: NO), then, the ECU 10 determines whether the regeneration duration TRdpf is greater than a second predetermined value β in S130 as another determination of whether the oil dilution quantity Qd is greater than the predetermined quantity. During the regeneration of the DPF 9, the post-injection is performed continuously and there is a state where the oil dilution quantity Qd continues increasing. Therefore, the determination of the regeneration duration TRdpf can be used as a reference for determining whether the oil dilution quantity Qd reaches the predetermined value. When the regeneration duration TRdpf is long, there is a possibility that the oil dilution quantity Qd has increased significantly. Therefore, in such the case, the regeneration device is switched to inhibit the increase of the oil dilution quantity Qd.

If it is determined that the regeneration duration TRdpf is not greater than the second predetermined value β in S130 (S130: NO), the ECU 10 determines that the oil dilution quantity Qd is not greater than the predetermined quantity and operates a first regeneration device (REGENERATION I, in FIG. 3) in S140 to efficiently proceed the combustion of the particulate matters in the DPF 9.

FIG. 4A shows a relationship between a crank angle (CA) and an opening degree (i.e., a lift amount L) of the injector in the case of the first regeneration device. Points where the injector is open (i.e., points where the lift amount L is not zero) represent a pilot injection 61 for mixing an air and the fuel before ignition to suppress an engine operation sound, a main injection 62 for obtaining motive energy, a post-injection A 63 and a post-injection B 64 from the left side in FIG. 4A. The post-injection A 63 and the post-injection B 64 are performed to send unburned fuel into the DPF 9 as the fuel for combusting the particulate matters deposited on the DPF 9 after explosion. If the post-injection of a large fuel quantity is performed at once in the state where the piston has descended after passing the top dead center, the unburned fuel of the quantity larger than a predetermined quantity will adhere to the cylinder wall, causing the increase in the oil dilution quantity Qd. As contrasted thereto, by dividing the post-injection, the post-injection quantity per injection can be reduced and the cylinder volume with respect to the fuel can be increased. This leads to reduction of the unburned fuel adhering to the cylinder wall and reduction of the oil dilution quantity Qd. TDC (Top Dead Center) In FIG. 4A represents the top dead center of the piston. In the present embodiment, FIG. 4A shows that the main injection 62 starts immediately after the top dead center.

In FIG. 4A, the post-injection A and the post-injection B are performed at timings considerably later than the main injection 62. Since the fuel reaching the DPF 9 without being combusted can be increased by delaying the injection timing, the particulate matters in the DPF 9 can be efficiently combusted with the comparatively small quantity of the post-injection. However, since the injection is performed in a state where the temperature in the cylinder is comparatively low, the unburned fuel reaching the cylinder wall increases and causes the increase of the oil dilution quantity Qd.

If the unburned fuel reaching the DPF 9 increases, the injection quantity or the time number of the post-injection until the fuel of a predetermined quantity reaches the DPF 9 reduces, alleviating the deterioration of the fuel consumption.

Then, the ECU 10 determines whether the particulate matter deposition quantity PM has sufficiently decreased through the regeneration of the DPF 9 in S160. The determination is performed using the publicly-known technology like S100. When it is determined that the particulate matter deposition quantity PM decreases sufficiently in S160 (S160: YES), the ECU 10 ends the regeneration of the DPF 9. When it is determined that the particulate matter deposition quantity PM has not decreased yet in S160 (S160: NO), the ECU 10 returns to S120 to perform the regeneration of the DPF 9.

If it is determined that the oil dilution quantity Qd is greater than the predetermined quantity in S120 (S120: YES), the ECU 10 operates a second regeneration device (REGENERATION II in FIG. 3) to alleviate the increase in the oil dilution quantity Qd in S150.

FIG. 4B shows a relationship between the crank angle (CA) and the opening degree (i.e., the lift amount L) of the injector in the case of the second regeneration device. It is shown that the timing of the post-injection is earlier in the case of FIG. 4B than in the case of FIG. 4A. Since the timing of the post-injection is advanced, the post-injection is performed while the pressure in the cylinder is high as compared to the case of the first regeneration device. Accordingly, the fuel reaching the cylinder wall reduces in quantity and the increase in the oil dilution quantity Qd is alleviated.

However, since the injection timing is early and the fuel is injected while the cylinder internal temperature as of the post-injection is high, part of the fuel of the post-injection combusts. Although this combustion produces the engine output, the combustion efficiency lowers and the fuel consumption deteriorates because the combustion occurs at the timing largely delayed from the top dead center. The amount corresponding to the combustion efficiency lowering is discharged as heat energy from the engine to the exhaust gas but part of the heat escapes from the exhaust pipe to the ambient air before the heat reaches the DPF 9. Therefore, the ratio of the fuel effectively used in raising the temperature of the DPF 9 out of the fuel of the post-injection decreases as compared to the case of the first regeneration device, deteriorating the fuel consumption.

An example of comparison of the cylinder internal temperature Tcyl as of the post-injection between the first regeneration device and the second regeneration device is shown in FIG. 5A. An example of comparison of the oil dilution quantity Qd between the first regeneration device and the second regeneration device is shown in FIG. 5B. An example of comparison of the fuel consumption F between the first regeneration device and the second regeneration device is shown in FIG. 5C. In each of FIGS. 5A to 5C, I corresponds to the first regeneration device and II corresponds to the second regeneration device. As shown in FIGS. 5A to 5C, the cylinder internal temperature Tcyl and the fuel consumption F are higher in the case of the second regeneration device than in the case of the first regeneration device but the oil dilution quantity Qd is higher in the case of the first regeneration device than in the case of the second regeneration device.

After the ECU 10 performs the regeneration, the ECU 10 moves to S160 to determine whether the particulate matter deposition quantity PM has decreased sufficiently. If the ECU 10 determines that the particulate matter deposition quantity PM has decreased sufficiently in S160 (S160: YES), the ECU 10 ends the regeneration of the DPF 9. If the ECU 10 determines that the particulate matter deposition quantity PM has not decreased sufficiently yet in S160 (S160: NO), the ECU 10 returns to S120 to select the regeneration device based on the oil dilution quantity Qd.

If it is determined that the regeneration duration TRdpf is greater than the second predetermined value β in S130 (S130: YES), the ECU 10 determines that the oil dilution quantity Qd has increased and operates the second regeneration device to alleviate the increase in the oil dilution quantity Qd in S150.

Next, a second embodiment of the present invention will be described. FIG. 6 is a flowchart showing regeneration processing of the DPF 9 according to the second embodiment. First, the ECU 10 calculates an oil evaporation quantity Qv in S200. The oil evaporation quantity Qv changes with an engine warming state (which is known from the engine coolant temperature Teng or the like) and the present oil dilution quantity Qd. The relationship among the oil evaporation quantity Qv, the engine warming state and the oil dilution quantity Qd is experimentally obtained beforehand and is stored in the ECU 10.

The increase of the engine coolant temperature Teng means increase of the temperature inside the engine. In such the case, the fuel in the oil evaporates easily, increasing the oil evaporation quantity Qv. If the oil dilution quantity Qd increases, the fuel evaporating from the oil also increases, so the oil evaporation quantity Qv also increases. FIG. 7A shows an increase in the oil evaporation quantity Qv due to the engine coolant temperature Teng and the oil dilution quantity Qd. In FIG. 7A, equal oil evaporation quantity lines are drawn. The oil evaporation quantity Qv is the same on each equal oil evaporation quantity line. The oil evaporation quantity Qv increases if at least one of the engine coolant temperature Teng and the oil dilution quantity Qd increases.

Then, in S210 of the flowchart, the ECU 10 determines whether the particulate matter deposition quantity PM of the DPF 9 is greater than a first predetermined value a requiring the regeneration of the DPF 9 as in the first embodiment. If it is determined that the particulate matter deposition quantity PM is greater than the first predetermined value a requiring the regeneration of the DPF 9 in S210 (S210: YES), the ECU 10 performs the post-injection to start the regeneration of the DPF 9 in S220. If it is determined that the particulate matter deposition quantity PM is equal to or less than the first predetermined value a in S210 (S210: NO), the ECU 10 enters a waiting state until the determination of whether the particulate matter deposition quantity PM is greater than the first predetermined value a requiring the regeneration of the DPF 9 is performed next time. The particulate matter deposition quantity PM is measured with a publicly-known technology, for example, as described in the description of the first embodiment.

Then, the ECU 10 starts the regeneration of the DPF 9 in S220. The processing in S220 is the same as S110 of the first embodiment.

Then, the ECU 10 calculates the oil dilution quantity Qd in S230. The oil dilution quantity Qd is related to the engine rotation speed NE and the output torque TOR. Also, the oil dilution quantity Qd is greatly influenced by the quantity of the post-injection. FIG. 7B shows an increase in the oil dilution quantity Qd due to the engine output torque TOR and the engine rotation speed NE. In FIG. 7B, equal oil dilution quantity lines are drawn. The oil dilution quantity Qd is the same on each equal oil dilution quantity line. The oil dilution quantity decreases if at least one of the engine output torque TOR and the engine rotation speed NE increases. When the engine rotation speed NE or the engine output torque TOR is low, the exhaust gas temperature TE is low. Therefore, in such the case, it is necessary to send a large quantity of the fuel into the DPF 9 for regenerating the DPF 9 through the post-injection. This causes a large quantity of the fuel to adhere to the cylinder wall, increasing the oil dilution quantity Qd.

Then, the ECU 10 calculates the quantity of the fuel presently diluting the engine oil from the oil dilution quantity Qd and the oil evaporation quantity Qv. The oil dilution quantity Qd represents the quantity of the fuel diluting the engine oil before evaporation. Therefore, the oil dilution quantity Qd also includes the quantity of the fuel evaporating after the dilution (i.e., the oil evaporation quantity Qv). The quantity of the fuel presently diluting the engine oil can be calculated by subtracting the quantity of the fuel evaporating after the dilution from the oil dilution quantity Qd. The ECU 10 determines whether the thus calculated quantity of the fuel diluting the engine oil is greater than a third predetermined value y in S240. In this way, as compared to the first embodiment, the quantity of the fuel diluting the engine oil can be calculated more accurately and the ECU 10 can select the regeneration device more suitably.

FIG. 8 shows a transition of the quantity of the fuel diluting the engine oil (i.e., the difference between the oil dilution quantity Qd and the oil evaporation quantity Qv) with respect to the travel distance (or travel time). Since the post-injection is performed during the regeneration period (R in FIG. 8), the quantity of the fuel diluting the engine oil increases. During a non-regeneration period (NR in FIG. 8), in which the regeneration is not performed, the post-injection is not performed. Therefore, the fuel diluting the engine oil only evaporates and the quantity of the fuel diluting the engine oil decreases. The ECU 10 switches the regeneration device from the first regeneration device I to the second regeneration device II when the quantity of the fuel diluting the engine oil exceeds a threshold value A. Thus, the increase in the quantity of the fuel diluting the engine oil is alleviated.

If it is determined that the quantity of the fuel diluting the engine oil is not greater than the third predetermined value y in S240 (S240: NO), the ECU 10 operates the first regeneration device in S250 to prioritize the inhibition of the fuel consumption deterioration and to proceed the combustion of the particulate matters in the DPF 9 efficiently. The processing performed by the first regeneration device is the same as the first embodiment.

Then, the ECU 10 determines whether the particulate matter deposition quantity PM has sufficiently decreased through the regeneration of the DPF 9 in S270. The determination is performed in the publicly-known method as in the first embodiment. If it is determined that the particulate matter deposition quantity PM has decreased sufficiently in S270 (S270: YES), the ECU 10 ends the regeneration of the DPF 9. If it is determined that the particulate matter deposition quantity PM has not decreased yet in S270 (S270: NO), the ECU 10 returns to S230 to perform the regeneration of the DPF 9.

If it is determined that the quantity of the fuel diluting the engine oil is greater than the third predetermined value y in S240 (S240: YES), the ECU 10 determines that the oil dilution quantity Qd is increasing and operates the second regeneration device in S260 in order to alleviate the increase in the oil dilution quantity Qd. The processing performed by the second regeneration device is the same as the first embodiment.

The above embodiments may be modified, for example, such that the oil dilution quantity Qd is calculated directly from viscosity of the engine oil by using an oil level sensor, a viscosity sensor or the like.

While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiments, it is to be understood that the invention is not to be limited to the disclosed embodiments, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims. 

1. An exhaust gas purification device of an internal combustion engine having a diesel particulate filter for collecting particulate matters contained in exhaust gas of the engine, the exhaust gas purification device comprising: a controller that controls operation of the exhaust gas purification device; a particulate matter deposition quantity measurement section that measures a deposition quantity of the particulate matters in the diesel particulate filter; a particulate matter deposition quantity determination device that determines whether the deposition quantity of the particulate matters measured by the particulate matter deposition quantity measurement section is greater than a first predetermined value; an oil dilution related data measurement device that measures oil dilution related data necessary for deriving an oil dilution quantity as a quantity of fuel diluting engine oil; an oil dilution related data determination device that determines whether the oil dilution related data measured by the oil dilution related data measurement device is greater than a second predetermined value; and a regeneration device that combusts the particulate matters to regenerate the diesel particulate filter, the regeneration device including a first regeneration device and a second regeneration device, which causes the oil dilution quantity less than the oil dilution quantity cause by the first regeneration device and causes a fuel consumption rate greater than the fuel consumption rate caused by the first regeneration device, wherein the controller has a selection device, the selection device selects the first regeneration device from the two regeneration devices when the particulate matter deposition quantity determination device determines that the particulate matters greater than the first predetermined value in quantity are deposited in the diesel particulate filter and the oil dilution related data determination device determines that the measured oil dilution related data is lower than the second predetermined value, and the selection device selects the second regeneration device from the two regeneration devices when the particulate matter deposition quantity determination device determines that the particulate matters greater than the first predetermined value in quantity are deposited in the diesel particulate filter and the oil dilution related data determination device determines that the measured oil dilution related data is higher than the second predetermined value.
 2. The exhaust gas purification device as in claim 1, wherein the first regeneration device performs post-injection for injecting the fuel in an expansion stroke, and the second regeneration device performs the post-injection at injection timing advanced from injection timing in the case of the first regeneration device in the expansion stroke.
 3. The exhaust gas purification device as in claim 1, wherein the post-injection is performed as a plurality of injections performed in a plurality of times during the expansion stroke.
 4. The exhaust gas purification device as in claim 1, wherein the oil dilution related data measurement device measures the oil dilution related data from vehicle speed and a travel distance in a period in which the first regeneration device or the second regeneration device is operated or from the vehicle speed and a travel time in a period in which the first regeneration device or the second regeneration device is operated.
 5. The exhaust gas purification device as in claim 1, wherein the oil dilution related data measurement device measures the oil dilution related data from a duration in which the first regeneration device or the second regeneration device is operated.
 6. The exhaust gas purification device as in claim 1, wherein the oil dilution related data measurement device derives the oil dilution related data from a difference between the oil dilution quantity and an oil evaporation quantity as a quantity of the fuel evaporating from the oil. 